1. Field of the Invention
The present invention relates to a base transceiver station employed in a radio communication system of a CDMA (Code Division Multiple Access) type, and particularly to resource management thereof.
2. Description of the Related Art
In a CDMA type radio system, various control information are transmitted as control channels, and user data such as voice data and packet data are transmitted as user channels. When such data are transmitted from a radio mobile station to a base transceiver station, the user channels are mapped onto an I axis and the control channels are mapped onto a Q axis respectively, followed by being QPSK-modulated in the mobile station. Further, they are subjected to spectrum spread modulation by spreading codes, followed by being transmitted to the base transceiver station. When the base transceiver station accepts a call from the mobile station, the base transceiver station receives the above spectrum spread modulated signal from the mobile station, despreads the control channels on the Q axis using the same spreading codes as the mobile station, and despreads the user channels on the I axis. A spreading factor (SF) of each spreading code used as transmission rate information of the spectrum spread modulated signal at its reception is extracted from each of the despread control channels. Then, phase control and coherent detection of each data channel spread-processed according to a transmission rate are carried out, followed by demodulation to user data. The demodulated user data are subjected to decoding processing such as an error correction, error detection, etc. (refer to, for example, a patent document 1 (Japanese Unexamined Patent Publication No. 2001-267959)).
A conventional control method for the base transceiver station will next be explained.
Upon communications between a mobile station and a base transceiver station under a radio communication system, the base transceiver station performs the transmission/reception of control information using a common channel (control channel) where, for example, a connection request (call) from a mobile station takes place, and shares parameters necessary to set each dedicated channel (data channel). When radio resources (resources necessary for transmission/reception) necessary to set the dedicated channels, and channel resources (i.e., a despread unit, a demodulator, a decoder, a memory, etc.) for the base transceiver station can be ensured, the base transceiver station performs the setting of each dedicated channel to the mobile station having made the connection request and starts communications of user data with the mobile station.
The base transceiver station performs reception of call setting information and setting processing in accordance with instructions issued from a radio network controller (RNC) corresponding to its host device. If, however, there is not enough free space for the channel resource of the base transceiver station, then the base transceiver station sends back reception disable information that a new call cannot be accepted, to the corresponding mobile station upon reception of the new call and does not perform the setting processing.
Thus, in order to make it possible to determine whether the call should be accepted, the base transceiver station performs the management of channel resources accommodable (i.e., allocable to a mobile station in which a call has occurred newly) therein. Such management relates to hardware and software processes, which are managed by the number of resources in advance every transmission rates available for uplink communications. Since the limited resources are applied statically in this management, a resource allocated to a call is not applicable to other call until the call is set free.
With the management of each resource in this way, a transmission rate of a communication signal (i.e., the above spectrum spread modulated signal) on a radio channel for a new call is detected when the new call is made. A decision is made as to whether the reception of this call is enabled according to whether the number of resources necessary for the transmission rate exists. However, the maximum transmission rate available for a set radio channel (channel corresponding to a spreading code in the CDMA system) is used as a transmission rate defined as a criterion as to whether the allocation of such resources is enabled. Even though the transmission rate becomes maximum among all held (i.e., set) radio channels, processes such as despreading, demodulation, decoding or the like of received user data on respective radio channels are performed without any delay so as to make it possible to ensure resources.
However, the uplink information (user data) decoded by the base transceiver station differ in parameter upon error correction processing or the like used in decoding processing, according to the type of applied data. With the difference between the parameters, resources for hardware to be utilized differ. Therefore, when a change in the type of data occurs in the uplink information from the mobile station to the base transceiver station where the uplink information is decoded, the resources for the hardware are switched on each occasion. The number of resources allocable to the corresponding radio channel is determined in consideration of even such a thing. Thus, the number of resources for the hardware is distributed to the mobile station having produced a call for a new connection request by giving consideration even to that a change in data type thus occurs in uplink information to be transmitted from now on. However, whether the number of resources should be distributed thereto (i.e., whether this call should be accepted) depends upon whether the number of resources available for the hardware at that time exists. That is, the number of processable channels differs depending on the number of resources for the hardware.
As a method for allocating the resource to the radio channel having accepted the call, there has been proposed a technique wherein a resource amount calculation table in which a symbol rate per each resource is represented by an uplink u-plane from a mobile station to a base transceiver station and a downlink u-plane from the base transceiver station to the mobile station, and a source amount calculation table indicative of the relationship between radio channel numbers and the number of resources are set, and a resource amount for the corresponding radio channel is allocated using such a resource amount calculation table (refer to, for example, a patent document 2 (Japanese Unexamined Patent Publication No. 2004-282469)).
According to the description disclosed in the patent document 2, a resource management table showing the relationship between signal processors and the number of resources available with respect to the same is set to perform resource management. The resource management table is retrieved based on the resource amount of the corresponding radio channel determined using the resource amount calculation table, and a signal processor having a vacant resource processable for the present radio channel can be selected.
When the radio channels are subjected to decoding processing (such as the settings of processing timings for a plurality of radio channels where the plurality of radio channels are decoded) by software, algorithms applied to the decoding are different in terms of the type of data or the like. Due to the difference between such algorithms, the time required to complete the decoding processing varies. Therefore, the number of channels accommodable (i.e., processable simultaneously) in the base transceiver station is not uniquely determined from only the transmission rate of each radio channel. Therefore, the storage capacity of the base transceiver station depends upon the throughput capacity of the decoder to make the best use of it. However, there is a need to define in advance the distribution of the number of resources set every data type applied to each radio channel, to the corresponding demodulator.
According to the above method for allocating the resources to the radio channels, even though the possible maximum transmission rate of each radio channel to which wireless communications are set is assumed, and the transmission states of all radio channels are simultaneously brought to the state of the maximum transmission rate, the storage capacities of hardware and software enough to simply enable the completion of processing within a prescribed time over all the radio channels. Therefore, the number of resources corresponding to each of the maximum transmission rates is allocated to each of these all radio channels.
On the other hand, the radio communication system such as the CDMA system or the like performs the transmission of user data through radio channels between the mobile station and the base transceiver station only where the transmission of the user data is required, in order to make good use of the limited radio resources. When there is no user data to be transmitted, the transmission of only the minimum information, i.e., control channels necessary to maintain the connections of the radio channels is performed. Described specifically, a transmission rate on a radio transmission line between a mobile station and a base transceiver station is reduced. Further, only closed-loop transmit power control information and transmission rate information used to control and hold transmit power between the mobile station and the base transceiver station to a proper value, and an identifier of a transmission rate, which is capable of identifying the presence or absence of user data, are repeatedly transmitted and thereby the connections of the radio channels are maintained.
Incidentally, voice data, packet data and the like are considered as the user data applied to such a radio communication system. However, when, for example, transmit user data on a radio channel is of voice data, a silent section exists about 50%. When the silent section is detected, the transmission of user data onto its corresponding radio transmission line is stopped on the transmitter side (the state of transmission of the user data is discontinued), and only control information such as the transmit power control information or the like on the radio channel is transmitted. Even in the case of the packet data, communications are carried out at a high transmission rate only where the acquisition of desired data such as download is required. When the acquisition of data is not necessary, the transmission of user data through the radio transmission line is stopped in a manner similar to the voice data, and the switching of a transmission state is performed in such a manner that only the control channel is transmitted at a low transmission rate. Thus, control on the switching of the transmission rate is dynamically carried out according to the presence or absence of the user data.
Thus, in the radio communication system for dynamically controlling the transmission rate, when the management of the channel resource (resource for the radio channel) in which its maximum transmission rate is assumed with respect to the radio channel as described above, is executed at the base transceiver station, data transmission is not carried out at all times at the maximum transmission rate over all the radio channels, and the transmission of data at the maximum transmission rate is rather rare. Therefore, a problem arises in that even though the number of resources is allocated to each radio channel according to the maximum transmission rate, at least some thereof is not used and the processing performance of the base transceiver station is not used to the fullest extent.